Method and apparatus for grinding rubber

ABSTRACT

A rubber grinding machine and method is provided for ambient temperature grinding of rubber material to form finely ground rubber particles. The rubber grinding machine includes a feed tube, a grinding module, a conveyor, a screening module and a vacuum system. Rubber material is placed in the feed tube which advances the rubber material into the grinding module using a plunger or auger. The grinding module includes a grinding wheel which grinds the rubber material into rubber particles. The grinding wheel is surrounded by a shroud which includes a water-cooled cooling jacket. The water is circulated through the cooling jacket to cool the shroud and its interior. Rubber particles ground by the grinding wheel fall through the bottom of the shroud onto a conveyor which deposits the rubber particles onto the screen module. The screen module includes at least one screen for separating the rubber particles by size. Rubber dust produced by the grinding wheel is processed by a vacuum system and may later be screened.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a rubber granulating machine andmethod, and more particularly to a process and apparatus for grindingrubber or similar material. The rubber or similar material is groundinto a usable or marketable end product such as rubber powder that maybe used in the rubber industry.

[0002] The disposal or reuse of previously used rubber products, such asrubber tires, presents many problems. Ecologically, rubber tires degradevery slowly and if disposed of improperly, may lead to hazardousenvironmental conditions in terms of both potential ground waterproblems and other ecological effects. Recently, recycling of pre-usedrubber products has increased in popularity in order to avoid potentialnegative environmental impact as well as to provide potentiallycommercially reusable rubber products.

[0003] Several methods for recycling used rubber products exist. Often,rubber products such as rubber tires are rendered into dust or fineparticulate rubber which then may be reused in other rubber products.However, one of the difficulties with recycling rubber products such astires is that such products are extremely durable and consequentlydifficult to reduce to a re-usable form. In order for any recyclingeffort to be cost effective, a method must be developed to reduce theextremely durable rubber products to a form of rubber that may beuseable in further generating processes. Recycled rubber particlesbecome more commercially valuable with decreasing particle size. Thecommercial value increases because rubber particles of smaller sizes maybe more easily incorporated into a wider variety of new rubber products.

[0004] U.S. Pat. No. 4,813,614 issued to Moore et al. entitled, “Methodand Apparatus for Treating Waste Products to Recover the ComponentsThereof” illustrates an early method for recovering rubber particlesfrom pre-used rubber products such as tires. In Moore, used productssuch as used rubber tires are frozen using liquid nitrogen and are thencrushed. The particles are re-frozen and re-crushed in successive stagesto yield finer and finer rubber particles. The crushed output is thenseparated with regard to the size of the crushed particles and crushedparticles may then be sold and/or reused based upon their size. In orderto lower the temperature of the rubber tires sufficiently so that therubber tires behave more solidly and less elastically so that the rubbertires may be crushed, Moore relies on a large quantity of liquidnitrogen. Liquid nitrogen is, of course, expensive to use. Thus,although the Moore process may yield fine particulate rubber, it isquite expensive.

[0005] U.S. Pat. No. 5,695,131 issued to Wenzel entitled “ShredderSeparator” illustrates another device for recycling used rubber productssuch as rubber tires. The shredder separator of Wenzel includes a numberof rotating blades that cut or shred a tire into small pieces. Theshredding separator of Wenzel operates at ambient (i.e., generally roomtemperature) and thus avoids the expensive liquid nitrogen cooling stepsof Moore. However, the product output by Wenzel's shredder isundoubtedly inferior to the product output by Moore for use in newrubber products because of the larger output size of the rubberparticles. Because the shredder relies on a number of rotating bladesrather than successive crushing steps, the recycled rubber particles arefar larger than the rubber particles of Moore and consequently lesscommercially desirable for many applications. While large size particlesmay be suitable to such applications such as playground flooring and thelike, the output of Wenzel is less suitable for reconstitution into newrubber products. By comparison, the fine rubber particles of Moore maybe considerably more easily and economically incorporated into newrubber products.

[0006] U.S. Pat. No. 5,299,744 to Garmater entitled “GranulatingSeparating and Classifying Rubber Tire Materials” illustrates a furthersystem for recycling used rubber tires. As with Wenzel, Garmaterincludes a rotating cutter wheel for reducing large chunks of tire intosmaller chunks which may be reusable for some purpose such as groundcover for playgrounds, jogging trails, and the like. As with Wenzel, therubber particles produced by Garmater are fairly large and maybesuitable for ground cover applications rather than applications such asreconstitution into new rubber products.

[0007] Thus, rubber recycling reclamation or granulating machines may beclassified into two types. A first type produces fairly large rubberparticles and operates at room temperature, often using rotating knivesor knives of some sort to produce the particles. The process is fairlyinexpensive. However, the large rubber particles produced, while usablefor applications such as ground cover, are not generally usable for morecommercially desirable applications such as new rubber products. Asecond type of rubber reclamation is the type shown in Moore in whichthe machinery operates at extremely lower temperatures and produces fineparticles. Because the process operates at low temperatures, the processis fairly expensive. The rubber particles produced, however, may beemployed in new rubber products.

[0008] Additionally, although the processes of Wenzel and Garmater mayproduce some small amount of fine particles, for example as a byproductof the process, such particles are a very small fraction by weight ofthe output of the process. Only a small fraction of the total rubbermaterial processed using the processes of Wenzel or Garamater may yieldfine particle sizes.

[0009] Thus, a need exists for an improved method and apparatus forreducing rubber products such as pre-used rubber products, into finegrain particles with a high process efficiency. A need has especiallyexisted for such a method and apparatus able to operate with lower cost.

[0010] It is therefore an object of the present invention to minimizethe expense of producing commercially reusable rubber particles byproviding a cost-effective, generally ambient temperature process thateliminates costly liquid nitrogen freezing.

BRIEF SUMMARY OF THE INVENTION

[0011] These and other objects are accomplished in a rubber grindingmachine and method which operates at generally ambient temperature andproduces fine grain rubber particles at a low cost. Rubber materialadvances into a grinding module where the rubber material is ground intorubber particles via a rotating grinding wheel. A shroud surrounds thewheel to capture and direct the ground material as well to cool thegrinding wheel. Rubber particles ground by the wheel gravitate throughthe bottom of the shroud and onto a conveyor. The conveyor moves theparticles into a screen module where the particles are separated bysize. Rubber dust produced by the grinding wheel is collected by avacuum system and may be later screened as well.

[0012] Thus, finely ground rubber particles are created which aresuitable for incorporation into new rubber products. The rubberparticles are produced cheaply and efficiently.

[0013] These and other features of the present invention are discussedor apparent in the following detailed description of preferredembodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014]FIG. 1 is a perspective view of an embodiment of a rubber grindingmachine according to the present invention.

[0015]FIG. 2 is a cutaway perspective view of a grinding module of themachine of FIG. 1.

[0016]FIG. 3 is a cutaway top view of the grinding module of FIG. 2.

[0017]FIG. 4 is a partial, cutaway side view of an alternativeembodiment of the machine of FIG. 1.

[0018]FIG. 5 is a perspective view of an alternative screening module ofthe machine of FIG. 1.

[0019]FIG. 6 is a perspective view of an alternative screening module ofthe machine of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

[0020] Referring to FIG. 1, Referring to FIG. 1, a rubber grindingmachine 100 includes a grinding module 110 where rubber is ground intofine particles. A pair of feed tubes 120 forces rubber material 111 intogrinding module 110, from which ground particles exit and aretransported via a conveyor 130 to a screening module 140. A dustcollection pipe 150 together with a cyclone air system 160 and a dustcollection bin 170 cooperate to collect rubber dust particles.

[0021] Referring to FIGS. 2 and 3, grinding module 110 includes an axle210 which drives a grinding wheel 220. Wheel 220 is affixed to axle 210which is rotated by a motor 113 (FIG. 1) and drive belt assembly 115(FIG. 1). If desired, another grinding module 117 (FIG. 1) may be drivenby axle 210, motor 113 and drive belt assembly 115.

[0022] An enclosed cylindrical shaped shroud 230 entirely encompassesthe grinding wheel as shown in FIGS. 2 and 3. A cooling jacket 240 ispositioned at the distal end of shroud 230 and cools the wheel duringthe grinding process. Cooling jacket 240 includes a plurality of waterinlet pipes 112 and a plurality of water outlet pipes 114, of which twoof a preferred three are shown.

[0023] The cooling jacket 240 is formed by a pair of spaced apart,circular walls 241, 243 which create an open cylindrical cavity. Anumber of internal baffles 244 may be placed in the jacket between walls241, 243 and may aid in assisting heat transfer, and/or providingstructural support to the jacket. Cold water or other liquid isintroduced into cooling jacket 240 through water inlet pipes 112. Thewater or other liquid exits cooling jacket 240 through water outletpipes 114.

[0024] As shown in FIG. 2, feed tubes 120 pass completely throughcooling jacket 240 and have each of their terminal ends 121 disposed ina plane adjacent the general plane of the outer surface 221 of grindingwheel 220. Each feed tube 120 is cylindrical in shape having its centeraxis parallel to the axis 311 (as shown in FIG. 3) of grinding wheel220.

[0025] A pair of plungers 122 are slidably disposed in tubes 120. Eachplunger 122 includes a circular disk mounted at a distal end and sizedto move along the inner surface 123 of the tubes. A portion of each tube120 is removed to provide a feed location 124 where rubber material maybe manually inserted into the tube. Each plunger is pneumatically drivenby pneumatic cylinders 125, 127 (FIG. 1).

[0026] In operation, rubber material is loaded into the material feedlocations 124 of the feed tubes 120 as shown. Plungers 122 of the feedtubes advance the rubber material toward grinding wheel 220 of grindingmodule 110. Plungers 122 press or force the rubber material against theouter surface 221 of grinding wheel 220 causing the rubber material tobe ground up into fine rubber particles. Grinding wheel 220 generatesrubber dust as well as other sized particles of rubber material.

[0027] The terminal edges of the feed tubes 120 are generally in contactwith outer surface 221 of the grinding wheel, as shown in FIG. 3.However, the outer surface 221 of grinding wheel 220 is not flat, buthas a grinding grain. Because the grinding surface 221 is not flat, thecontact between the edges of the feed tubes 120 and the surface 221 isnot continuous. As the wheel rotates, gaps develop between the edges ofthe feed tubes 120 and the grinding wheel 220 and allow ground rubberparticles to escape from the feed tubes 120 and into the shroud 230.

[0028] In operation, the shroud 230 and the grinding wheel 220 arecooled by water flowing through the cooling jacket 240. The grinding ofrubber by the grinding wheel 220 produces heat or thermal energy. Thethermal energy heats the interior space of the shroud 230 and the shroud230 itself. The shroud 230 and the cooling jacket 240 are preferablycomposed of a thermally conductive material, such as steel.

[0029] Cooling jacket 240 is physically directly connected to the shroud230 and is thus thermally coupled to the shroud. The cooling jacket 240is cooled by the flow of water through the cooling jacket 240. Becausethe cooling jacket 240 is thermally coupled to the shroud 230, the flowof water into and out of the cooling jacket 240 cools the shroud 230 andits interior space.

[0030] The circulation of water through cooling jacket 240 via the inletand outlet pipes serves to maintain the cooling jacket 240 at a lowtemperature thus providing cooling to the entire grinding module 110.The cooling provided by the cooling jacket allows the grinding to beperformed at generally room temperature without expensive coolingsystems. The present invention is thus considerably more cost effectivethan prior art system relying on freezing systems or liquid nitrogen.

[0031] Referring again to FIG. 1, once the rubber material has beenground by grinding wheel 220, the ground rubber material falls throughan aperture 131 formed in the lower section of shroud 230 and ontoconveyor 130. Material falling onto the conveyor 130 is moved by theconveyor to screening module 140. At the screening module 140, theground rubber material falls from the conveyor 130 onto a screen 142which is disposed on top of a retention bin 144. Screen 142 extendscompletely across the top of retention bin 144. Screen 142 has uniformapertures of a size chosen so that larger pieces of rubber material areunable to pass through screen 142 so as to be separated on top of theretention bin 144. Larger particles may be sorted for sale, or may bere-introduced into the material feed location 124 of a feed tube 120 toproduce smaller particles. Smaller pieces of rubber material fallthrough the screen 142 to a lower level of the retention bin 144 wherethe particles may be removed via an output 146.

[0032] Overly large particles may be blocked by the screen 142 whileparticles of an acceptable size may fall through the screen 142. Thescreening module 140 may include another screen (not shown), orientedlike the screen 142 and vertically disposed in a horizontal planebetween the first output 146 and a second output 148. The second screenmay be composed of a finer mesh in order to further separate groundrubber particles based on size. Rubber particles that are too large topass through the second screen may be removed from retention bin 144through output 146. Rubber particles that are small enough to passthrough the second screen may be removed from the retention bin 144through a second output 148.

[0033] The action of the grinding wheel 220 generates a rubber “dust orpowder.” The rubber dust may include rubber particles that have beenreduced to a size where the force of air motion, such as the air motiongenerated by the grinding wheel 220, temporarily overcomes the force ofgravity on the rubber particle and the rubber particles become airborne.The present invention preferably yields 95%-97% dust at 70 mesh minus.Seventy mesh minus is a term of the art indicating that the dust willpass through a one-square-inch mesh of 70 holes horizontally by 70 holesvertically. The present invention yields at least 40 mesh minus dustparticles.

[0034] Referring to FIG. 1, the conveyor 130 may be enclosed in whole orpart. An enclosure 131 which is U-shaped in configuration, directs thedust particles to the dust collection pipe 150. Airborne dust is pulledalong the enclosure 131 and into the dust collection pipe 150 by airpressure generated by a vacuum system, preferably a cyclone air system160. The dust collection pipe 150 conveys dust to the cyclone air system160 where the dust is circulated inside the dust collection bin 170 andreclaimed. As the cyclone system 160 circulates the dust, the dustempties into the dust collection bin 170 which is preferably a 55-gallondrum. The dust collection bin 170 preferably forms a packaging containersuch as a 55-gallon drum or other packaging container so that thepackaging container and enclosed dust may be easily transported andsold. Additionally, rubber dust particles may be further screened beforebeing packaged and sold. Particles larger than a desired size may bere-introduced to the grinding module. The shroud 230 is directlyconnected to the enclosure 131 as shown. The enclosure 131 preferablyoverlaps the edges of the conveyor 130 and may preferably extendunderneath the upper belt of the conveyor 130 as shown.

[0035]FIG. 4 illustrates another embodiment of a feed tube 400. Insteadof the plunger 122 of FIGS. 1-3, feed tube 400 includes an auger 410 anda material feed port 420. In operation, material 421 is added to thematerial feed port 420. The material falls into the auger 410. As auger410 is rotated about its axis, the material is advanced by the rotationof the auger and forced into contact with the grinding wheel 220.

[0036]FIG. 5 illustrates an alternative screening module 500. Thescreening module is rectangular in shape as opposed to the circularshape of the screening module 140 of FIG. 1. The screening module 500includes an upper screen 510, a lower screen 520, a first rubberparticle outlet 530 and a second rubber particle outlet 540. Similar tothe screening module 140 of FIG. 1, ground material is relayed from thegrinding module 110 to screening module 500 via conveyor belt 130. Aswith the screening module 140 of FIG. 1, ground material falls uponupper screen 510. Material that is too large to pass through the upperscreen 510 remains on top of the upper screen 510. Material small enoughto fit through the screen 510 falls through the upper screen 510 and isincident upon the lower screen 520. Material that is small enough passesthrough the lower screen 520. Material passing through the upper screen510 but not passing through the lower screen 520 is removed from thescreening module 500 via the first rubber particle output 530. Materialpassing through both the upper screen 510 and the lower screen 520 isremoved from the screening module 500 via the second rubber particleoutput 540. Preferably the screening module 500 is approximately fourfeet wide by 25 feet in length. The mesh of the upper screen 510 mayhave a mesh size and the mesh size may be one of several sizes rangingdown to preferably 70 mesh. The lower screen may also range in mesh downto 100 mesh. As will suggest itself, screening module 500 may be shakenby means (not shown) to facilitate screening.

[0037]FIG. 6 illustrates another alternative exemplary screening module600. The screening module 600 is rectangular in shape, similar to thescreening module 500 of FIG. 5, and is in the form of a shaker table.The screening module 600 is shaken and the ground material flows in thedirection of the arrow 615. The screening module 600 includes a mainscreen 610; four sub-screens 620, 630, 640, 650; and four particleoutput shoots, 625, 635, 645, 655. Similar to the screening module 500of FIG. 5, ground material is relayed from the grinding module 110 toscreening module 600 where the ground material falls upon the mainscreen 610. Material that is too large to pass through the main screen610 remains on top of the main screen 610 and may be periodicallyretrieved and re-introduced into the grinding module 110.

[0038] Material small enough to fit through the main screen 610 fallsthrough the main screen 610 to the sub-screens 620, 630, 640, 650. Thesub-screens 620, 630, 640, 650 may be screens of different sizes witheach sub-screen 620, 630, 640, 650 positioned on top of a singlechamber. For example, when material is added to the screening module 600in the flow direction 615, material falls downwardly onto sub-screen 650and then moves laterally across sub-screens 640, 630 and 620 insuccession. Sub-screens 620, 630, 640, 650 are ordered so that thesub-screen 650 has the smallest mesh and that sub-screens 640, 630, and620 have consecutively larger meshes. Thus, the exemplary screeningmodule 600 may separate material into five sizes, a first size too largeto pass through the main screen 610, and four consecutively smallersizes, corresponding to the four sub-screens 620, 630, 640, 650.Material may be removed from the chamber below each sub-screen 620, 630,640, 650 using the corresponding particle output shoot 625, 635, 645,655.

[0039] The present invention thus provides an improved machine andmethod for reducing rubber, and similar material products such aspre-used rubber products, into fine grain particles. The presentinvention is especially cost effective because the present invention mayproduce fine particles suitable for incorporation into new rubberproducts without using the expensive cooling and freezing processes ofthe prior art. The present invention operates at generally ambienttemperatures thus alleviating the need for expensive liquid nitrogenfreezing steps, while providing a high percentage of finely groundrubber particles usable in many commercial applications.

[0040] While particular elements, embodiments and applications of thepresent invention have been shown and described, it is understood thatthe invention is not limited thereto since modifications may be made bythose skilled in the art, particularly in light of the foregoingteaching. It is therefore contemplated by the appended claims to coversuch modifications and incorporate those features which come within thespirit and scope of the invention.

1-21. (canceled).
 22. A method for grinding recyclable productscomprising the steps of: advancing recyclable material onto a solidgrinding wheel, wherein said grinding wheel is surrounded by a shroud;grinding said recyclable material with a said grinding wheel to producerecyclable particles; and cooling said grinding wheel using a coolingjacket thermally coupled to said shroud.
 23. The method of claim 22wherein said advancing step includes advancing recyclable material usinga plunger.
 24. The method of claim 22 wherein said advancing stepincludes advancing recyclable material using an auger.
 25. The method ofclaim 22 wherein said cooling step includes cooling using aliquid-cooled cooling jacket.
 26. The method of claim 22 wherein saidcooling step includes cooling using a cooling jacket including at leastone liquid inlet and at least one liquid outlet to allow circulation ofliquid within the cooling jacket.
 27. A method for recycling rubbermaterial using a grinding wheel comprising the steps of: advancingrubber material against a solid grinding wheel, wherein said grindingwheel is surrounded by a shroud; grinding said rubber material intorubber particles; cooling said grinding wheel using a cooling jacketthermally coupled to said shroud; conveying said rubber particles awayfrom said grinding wheel; and separating said rubber particles based onsize.
 28. The method of claim 27 wherein said cooling step includescooling using a liquid-cooled cooling jacket.
 29. The method of claim 27wherein said cooling step includes cooling using a cooling jacketincluding at least one liquid inlet and at least one liquid outlet toallow circulation of liquid within the cooling jacket.
 30. The method ofclaim 27 wherein said screening step includes screening rubber particlesbased on size using at least two screens.
 31. The method of claim 27further including the step of processing airborne rubber particles usinga vacuum system.
 32. (canceled)
 33. A method for grinding recyclableproducts comprising the steps of: advancing recyclable material onto asolid grinding wheel, wherein said grinding wheel is surrounded by ashroud; grinding said recyclable material with said grinding wheel toproduce recyclable particles; and cooling said grinding wheel using acooling jacket in thermal contact with said shroud.
 34. A method forrecycling rubber material using a grinding wheel comprising the stepsof: advancing rubber material against a solid grinding wheel, whereinsaid grinding wheel is covered by a shroud; grinding said rubbermaterial into rubber particles; cooling said grinding wheel using acooling jacket in thermal contact with said shroud; conveying saidrubber particles away from said grinding wheel; and separating saidrubber particles based on size.
 35. A method for producing commerciallyusable rubber particles from used rubber material comprising:substantially powderizing used rubber material using a solid grindingwheel that is surrounded by a shroud, said powderizing taking place atsubstantially ambient temperatures; and cooling said grinding wheelusing a cooling jacket in thermal contact with said shroud.